As is well known by those skilled in this technology minimally invasive approaches for performing spinal surgery such as laminotomy, medial facetectomy, foraminotomy, nerve root retraction, discectomy and the like, require an initial cut into the skin and tissue of the patient before a series of increasingly larger diameter dilators are inserted to widen the area where the surgery will be performed. As is well known and as described in U.S. Pat. No. 6,159,179 granted on Dec. 12, 2000 to the inventor of this patent application and entitled “Cannula and Sizing and Insertion Method”, a guide wire with a sharpened tip to purcutaneously pass through the muscle and engage a target of bone or vertebral disc is typically used. The first dilator is then passed over the guide wire and down to the target. Unfortunately, this method is fraught with a potential danger to the patient. Because the guide wire is relatively thin where it is able to pass through the muscle and ligamentous anatomy, it can protrude into the spinal canal and hence, cause injury to the delicate neural anatomy. If the misplaced guide wire is not detected before the dilators are inserted, catastrophic injury, such as permanent disablement of the patient can occur. Obviously, since this is a potential problem as it is considered a risk to a candidate needing minimally invasive surgery, the use of this type of surgery has been stifled and its potential to grow which ultimately is for the benefit of all patients requiring this type of surgery is thwarted. Of course, the surgical target does not involve the neural anatomy in every spinal surgery and hence, in these situations the use of a guide wire is not a potential hazard and can be safely used.
I have found that I can obviate the problems noted in the above-paragraphs particularly in minimally invasive spinal surgery where it is necessary to access and decompress the spinal nerves and where safety is of a major concern. This invention utilizes a series of muscle dilators in which the first dilator is solid with a design that permits accurate passage through the muscle tissue without the assistance and risk of a pre-placed guide wire. The tip of this inventive dilator is judiciously designed to part and pass through the muscle fibers and allows the surgeon to maintain a course directed toward the intended anatomical target. Because of the inventive dilator when the muscle is passed in the insertion procedure the likelihood for the surgeon forcing the inventive dilator through the ligamentum flavum and continue to pass into the spinal canal is avoided. My invention contemplates dimensioning the non cannulated dilator such that the surgeon when performing the procedure will get a “feel” as the instrument passes through the tissue and muscle of the patient so that the surgeon will have a good sense of what portion of the anatomy is being penetrated. This will help in assisting the surgeon in avoiding the spinal canal.